Thermoelectric conversion elements for converting thermal energy to electrical energy are disclosed in the Patent documents 1 to 3. Those thermoelectric conversion elements are configured such that a p-type semiconductor material is joined with an n-type semiconductor material via metal or the like, and when the joint part is heated, power is generated according to the Seebeck effect. Bi—Te based materials are used as the p-type semiconductor material and the n-type semiconductor material.
On the other hand, as a system for converting energy from sunlight to electrical energy, there is disclosed a solar battery that utilizes a silicon semiconductor and a compound semiconductor, as described in the Non Patent Documents 1 to 3.
In addition, there is disclosed in the Patent Document 4, a solar heat collecting and power generation technique in which sunlight is converted to heat, and the heat allows water to vaporize, thereby rotating a turbine to generate power. This technique uses a receiver inside of which heat media (sodium nitrite 40%, sodium nitrate 7%, and potassium nitrate 53%) are arranged for collecting heat from sunlight, a heliostat for tracking sunlight to collect light, and the like.